To comprehend the neural basis of visual perception, it will be necessary to determine how information from sensory regions of the brain influences the neural circuitry that governs behavior. The brain acquires visual information and then interprets this information to decide its significance. A decision process thus intervenes between visual sensation and visually guided behavior. In the past five years, neurons have been identified in the parietal and frontal lobes of the monkey that represent the formation of a perceptual decision about the direction of visual motion in simple discrimination task. These neurons associate visual information with a planned behavioral response. They thus provide an unrivaled opportunity to study the formation of a decision at the neural level. Preliminary findings have shown that decisions about the direction of visual motion benefit from the integration of information as a function of time. The proposed experiments test the hypothesis that neurons in the association cortex compute the time integral of appropriate sensory information from the visual cortex and combine this information with prior bias in order to reach a decision. These experiments combine neural recording and stimulation with behavioral measurements of the speed and accuracy of visual perception. Three specific aims are planned. 1) Microstimulation of area MT will elucidate how changes in the representation of direction influence the perception of direction and the time required to reach a decision. 2) Neural recordings in area LIP will reveal the mechanism of the accumulation of motion information toward a decision. 3) Neural recordings in area LIP combined with behavioral manipulations of reward and prior bias will reveal the integration of psychological variables with visual information in decision formation. The integration of information to guide decisions is likely to be common to many aspects of cognition. Understanding the neural mechanisms that underlie a visual decision will thus help to elucidate the neural basis of cognition and its disorders. Such understanding promises to provide the means to promote recovery of both sensory and intellectual function in the face of neurological disease.